The growth of commercial radiocommunications and, in particular, the explosive growth of cellular radiotelephone systems have changed the ways in which people communicate. Many of the people who purchase mobile communication units and service subscriptions do so to enhance their personal security. Presumably, many of these subscribers expect to use their mobile units to aid them in urgent situations, e.g., when their vehicle has become disabled or in an emergency situation requiring rapid medical and/or police response. In these circumstances it is desirable that the radiocommunication system is able to independently determine a location of the mobile unit (also commonly called a user equipment (UE)), particularly in the case where the subscriber does not know his or her precise location. Moreover, many countries have implemented communications laws which require that radiocommunication networks possess a positioning capability that enables network operators to, for example, forward the position of an emergency caller to an emergency service provider.
There are many techniques available to generate mobile unit positioning information. In a first category, the mobile unit could estimate its own position and send a message with its coordinates when placing an emergency call or responding to a location request. This could be accomplished by, for example, providing the mobile unit with a Global Positioning System (GPS) receiver that receives location information from the GPS satellite network. The mobile unit can then transmit this information to the system, which would then forward it to the emergency service provider.
Alternatively, the base stations which transmit signals to, and receive signals from, the mobile units could be used to determine the mobile unit's location. Various techniques, including attenuation of a mobile unit's signal, angle-of-arrival, and difference between the time-of-arrival (TDOA) of a mobile unit's signal at different base stations, have been suggested for usage in providing mobile unit location information.
A third category of strategies for locating mobile units in radiocommunication systems involves the provision of an adjunct system, i.e., a system which may be completely independent of the radiocommunication system or which may share various components (e.g., an antenna) with the radiocommunication system but which processes signals separately therefrom. Such adjunct units are sometimes called Location Measurement Units (LMUs) and may or may not be physically co-located with the base stations in the radiocommunication networks. One drawback of using adjunct systems is the added cost associated with implementing a separate network solely for positioning purposes and the challenges associated with integrating the radiocommunication system with the separate adjunct system.
In the last 15 years or so since positioning has become a required capability for network operators and manufacturers, various positioning strategies have been selected for each standardized radiocommunication system. The particular selection of one or more positioning techniques for a given radiocommunication system is due, at least in part, to their compatibility with the underlying radio technologies used to establish voice and data connections in that radiocommunication system, as well as their accuracy and failure rates.
For example, in the next generation Long Term Evolution (LTE) system, the associated standard currently provides for positioning to be implemented using one of: an Observed Time Difference of Arrival (OTDOA) technique, an Assisted Global Navigation Satellite System (A-GNSS) technique, and an Enhanced Cell Identification (E-CID) technique. Generally speaking, the OTDOA technique involves the UE's measurement of downlink signals from various base stations (called eNodeBs in the LTE standard), the A-GNSS technique involves the usage of GPS signals by the UE, and the E-CID technique involves using the knowledge of which cell that the mobile station is currently located as a rough proxy for its current location. The interested reader can find more information about these current LTE positioning techniques in the standard document 3GPP TS 36.355 V9.0.0 (2009-12), entitled “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); LTE Positioning Protocol (LPP) (Release 9).
The positioning techniques currently selected for LTE suffer from some drawbacks. For example, OTDOA accuracy is limited by the UE's available processing power, A-GNSS suffers from relatively high failure rates in urban environments where the GPS signal penetration may be poor and E-CID is inherently a relatively low accuracy solution depending upon factors such as cell size. Thus it may be useful to consider enabling other, potentially higher accuracy positioning techniques to be usable in LTE systems.
One possibility is to use an uplink time of arrival or time difference of arrival positioning technique wherein adjunct units (e.g., eNBs and/or LMUs) measure a special signature transmitted by a UE when it is desirable to determine that UE's position. Such adjunct systems have been shown to provide relatively high positioning accuracy in older, e.g., time division multiple access (TDMA), radiocommunication systems. However, the reuse factor in such older radiocommunication systems was much higher than the reuse factor proposed for next generation systems, i.e., adjacent cells in next generation systems are intended to be able to reuse the same radio resources. This means that, on average, positioning signals transmitted on the uplink (i.e., UE to network direction) will experience significantly more intercell interference in next generation systems than they would have been expected to experience in older, e.g., TDMA, systems with higher reuse factors. Due to the high interference level, the failure rate of such uplink-based TOA or TDOA measurements in neighboring cells will, in operation, likely be unacceptably high for most implementations.
Accordingly, it would be desirable to provide devices, systems and methods for user equipment positioning which overcome the afore-mentioned drawbacks.